This invention pertains to the art of detecting and reporting devices and more particularly to method and apparatus for detecting and reporting some predetermined condition in a load bearing body.
The invention is particularly applicable to detecting a profile deflection greater than a maximum allowable amount in pneumatic vehicle tires and will be described with particular reference thereto. However, it should be appreciated by those skilled in the art that the invention has far broader applications and may be utilized in many other environments where it is desired to detect and report or indicate some predetermined profile deflection condition in a load bearing body.
Both overloading and under inflated conditions for pneumatic tires is a cause for excessive tire wear resulting in premature tire failure. Moreover, such overloading and/or under inflated tire conditions can have an adverse effect on the efficiency of operation of the vehicle as to both vehicle preformance and handling as well as vehicle gas mileage. Since such conditions and results have been well known for quite some time, there have been many attempts to develop and provide means for automatically detecting and reporting at least under and/or over inflation conditions. Recently, development efforts for a practical and inexpensive device for detecting tire conditions have become more concentrated due to the rise in fuel and tire costs as well as vehicle operation costs in general.
While there have been quite a number of prior devices developed and utilized for detecting tire inflation conditions, substantially all of these tire devices have had structural or operational shortcomings rendering them undesirable or impractical for widespread use. While these specific prior devices have been many and varied, most have required special wiring and the like extending from the wheel assemblies to the vehicle chassis and then through the vehicle body to the instrument panel. Such wiring adds undesired costs to the system and, moreover, is extremely difficult and time consuming to install. Such installation time is particularly important when considered both on the basis of installing the devices during original vehicle assembly for making them a part of the original vehicle equipment as well as retrofitting them. Further, the necessary special wiring and associated equipment extending between the wheels and chassis are such that they are susceptible to damage or breakage from road materials, weathering and the like encountered during normal vehicle use.
Some prior devices have attempted to overcome the aforementioned wiring problems by utilizing self contained units disposed at each wheel and which include small signal emitters such as radio transmitters. These emitters are energized to transmit a signal in response to the detection of some out of order tire condition and this signal is received in the vehicle to energize a convenient indicator device to advise the vehicle operator that an out of order tire condition is present. Such devices have utilized small batteries for providing a source of selective energization for the emitters. The problem encountered here is that batteries have an uncertain shelf and useful life and must be replaced from time to time. Since it is generally impossible to know when replacement is required, these prior devices have not proved to be reliable.
A still further and more important problem with apparatus and devices for detecting over and/or under inflated conditions in pneumatic vehicle tires is that the inflated condition is not always a true or accurate measure of actual tire condition. That is, a tire may be inflated to a pressure which is wholly within the tire manufacturer's specifications but, due to the load a particular vehicle may be carrying, the tire profile may be deflected to an unacceptable condition as prescribed by the manufacturer's specifications. One vehicle application where this situation could frequently arise would be in station wagon or truck type vehicles where the cargo portion of the vehicle was substantially loaded with heavy articles or equipment for transport from one point to another. Here, and while tire inflation or pressure may be proper, the profile deflection caused by the overloading is greater than the maximum allowable deflection so as to cause possible tire damage and/or vehicle handling problems.
In some overloading situations, it is possible to increase the tire inflation pressure to the maximum amount prescribed by the manufacturer's specifications with this increase in pressure acting so sufficiently reduce the amount of profile deflection so that it falls within acceptable limits. In heavy overloading conditions, however, such an increase in tire pressure will not reduce the profile deflection enough to bring it within acceptable limits so that a dangerous tire condition would still exist. Here, again, prior tire inflation sensing devices would only detect the fact that tire pressure was within allowable limits thereby giving the vehicle operator a false sense of security not only as to tire conditions, but also as to the handling and maneuverability of the vehicle.
As a result of the above noted problems encountered with prior inflation detecting equipment and the shortcomings of such devices insofar as the tire conditions which they actually monitor and/or detect, it has been desirable to develop apparatus and method which would sense tire profile conditions to thereby provide a better indication of both tire overloading and/or under inflation. Such method and apparatus should be self-contained, include no special wiring or associated equipment extending between the vehicle wheels and chassis, be simple and easy to install on a high vehicle production basis, have a long useful life, not require use of short lived power means such as batteries or the like, and be bi-directional, i.e., operate in both directions of wheel rotation.
The present invention contemplates new and improved apparatus and method which overcome all of the above referred to problems and others as well as meeting the above noted design criteria to provide a profile sensing device and method for hollow bodies. While the concepts of this apparatus and method are described with particular reference to implementation on a conventional vehicle wheel assembly, the inventive concepts are deemed to be readily adapted to use for any number of profile sensing functions for a hollow body in any number of environments.